1. Field of the Invention
The present invention relates to an apparatus and method for stabilizing the frequency of a laser, and particularly to an apparatus and method for stabilizing the frequency of a laser by feedbacking to correct frequency errors.
2. Description of Related Art
The application of a frequency-stabilized laser is very popular in the modern industry. The laser not only can be used in DWDM fiber communication, interferometer, spectrometer and so on, but also is an indispensable tool for many scientific researches.
A known method to stabilize a laser is to lock a laser in a cavity. However, due to extended usage and temperature variation of the cavity, a frequency drift of the laser occurs. To meet the requirement of extended usage, designers utilize atom""s or molecule""s spectrum as a reference, and a well-known example is a saturated absorption spectrum. However, the spectrum linewidth of the saturated absorption spectrum is so narrow, about several to hundreds of (MHz) that the range locked by this method is limited and the frequency lock always fails due to outside disturbance.
In other words, although a high stabilization can be obtained by the conventional method, the lasers can only be used in a laboratory due to complexity, a small range of locked frequency and bad noise immunity.
To solve the above problems, the present invention proposes a novel apparatus and method for stabilizing the frequency of a laser. The present invention has advantages of simple structure, a large range of locked frequency, a good noise immunity, and is suitable to a long-term use.
The present invention utilizes absorption spectrums to stabilize the frequency of a laser. To avoid the effect that a single-frequency absorption spectrum is easy to be affected by variations of laser power and the complexity to modulate the frequency of a laser, the present invention adopts at least two laser beams at different frequencies and obtains an error signal that is a difference in the absorption spectrums of laser beams. Since the error signal is a difference in two laser beams coming from an identical laser source, the variation of laser power could be eliminated. Furthermore, since the absorption spectrum is usually above hundreds of (MHz), the range of locked frequency of the present invention is large, and the laser frequency is not easily unlocked due to outside disturbance.